“They’re no longer together. They were never serious, though; it was just a casual thing and it fizzled,” one insider explains. “They were never in the same place at the same time.”

A second source adds: “Zac was never very serious about her. He didn’t talk about her to friends.”

The stars were first spotted holding hands during a friend’s birthday dinner at L.A. eatery STK February 8. After that, the low-key stars – who have been photographed together only once – only grew further apart.

“It’s true that their schedules are crazy right now, which isn’t conducive to a relationship being easy,” a pal tells Us.

Prior to his relationship with Collins, Efron was in a longterm relationship with his “High School Musical” costar Vanessa Hudgens, 23. Collins and her “Abduction” costar Taylor Lautner, 20, ended their courtship in September 2011. [Source]